Due to the extensive additional construction of wind turbines and wind farms, they are playing an increasingly important role in power generation on the electric grid. Grid operators are therefore requiring that wind farms also actively participate in regulation on the grid. Among other things, this relates to the provision of reactive power, but also to measures for monitoring the real power which is output. However, wind farms differ from conventional power plants in one important aspect; namely, the power output by them cannot be freely determined, but is a function of the wind speed in general and the wind conditions at the individual wind turbines on the wind farm in particular.
Generally, a setpoint specification for the power to be output is now transmitted to wind farms. Clearly, in the event of an increase in the power requirement, the wind farms are possibly only able to follow to a limited extent, depending on the wind conditions. However, in the event of a decrease in the power requirement, they are always able to respond, namely, by throttling the wind farm's wind turbine; thus, they do not fully exploit the available wind. In this direction, i.e., in the case of downward setpoint adjustments for the power, wind farms are in principle thus fully usable for grid regulation.
This is exploited by setting a setpoint value at the farm master for the power to be output. The farm master drives the wind turbine in such a way that corresponding power is generated and output to the grid, if the wind conditions permit it. If they do not permit it, the setpoint value is not reached, but the wind farm feeds in as much power as is currently possible.
If the grid operator now requires a reduction in the power output, the setpoint value provided to the farm master is correspondingly lowered. To avoid overshoots or undershoots in the power output, this generally is not carried out abruptly, but gradually as a ramp. The ramp-shaped reduction of the setpoint value also takes into account the fact that corresponding throttle signals must first be transmitted to the wind turbines distributed on the wind farm, and they must each individually adjust the pitch of their rotor blades in order to carry out the desired power reduction.
In the case of weak wind conditions, it is often the case that the power actually output is less than the setpoint value, i.e., the setpoint value is rather high. This discrepancy is unavoidable on a wind farm and is not problematic as such. However, in practice, problems occur if the setpoint value is significantly reduced starting from its rather high value. Due to the discrepancy with the much lower actual power output, the ramp-like decrease in the setpoint value initially has no effect at all, since the setpoint value is still above the actual value. The power output of the wind farm is actually reduced only if the setpoint value has decreased so much that it reaches the actual value and then decreases further. The wind farm thus responds to the requested power reduction in a delayed manner. There is an undesirable time lag. From the point of view of the grid operator, this is disadvantageous. However, it is even more disadvantageous for the grid operators that the length of the time lag is not fixed; rather, the greater that the discrepancy between the setpoint value and the lower actual power output initially was, the longer the time lag is. In terms of regulation, such behavior is difficult to manage and constitutes a risk for the system stability of the grid.